1. Filed of the Invention
This invention relates to pneumatic tires, and more particularly to a pneumatic radial tire for use in relatively small-size vehicles such as passenger cars, vans, pickups and the like simultaneously improving steering stability, road noise (hereinafter abbreviated as R/N) performance and ride comfort while dominantly holding tire weight, rolling resistance and the like.
2. Description of Related Art
In the pneumatic tires for automobiles, particularly tires for use in relatively small-size vehicles as mentioned above, it is demanded to improve various performances such as steering stability, ride comfort, indoor noise performance, fuel consumption (rolling resistance) and so on. Recently, it tends to more enhance the demand for simultaneously and highly improving the performances.
As regards such a demand, means for separately improving each of the performances is established as mentioned below. That is, there are the following means:
(1) means for improving steering stability: ensuring of cornering power, increase of tire rigidity, increase of hysteresis loss in tread rubber
(2) means for improving ride comfort and R/N performance: reduction of tire rigidity
(3) means for reducing weight and improving rolling resistance: reduction of tire rigidity, decrease of hysteresis loss in tread rubber
As mentioned above, it is possible to improve the individual performances. However, the means for improving the steering stability and the means for improving the ride comfort and R/N performance are quite conflicting with each other, so that it is obliged to adopt a temporary means such as gauge adjustment of tread rubber or the like in the present circumstances.
On the other hand, as the means for improving the steering stability without so degrading the ride comfort, there is proposed such a structure that a bottom width is made narrower and a height is made lower in a hard bead filler rubber and also a sheet-shaped rubber member having a hardness equal to that of the bead filler rubber is overlapped with the bead filler rubber at a top end portion thereof. Even in this means, the tire rigidity somewhat rises, so that there is still a problem that the ride comfort enough to satisfy the demand can not be obtained.
It is, therefore, an object of the invention to provide a pneumatic tire simultaneously and drastically improving the steering stability, ride comfort and R/N performance while ensuring at least an existing tire weight and holding an existing low rolling resistance.
According to the invention, there is the provision of a pneumatic tire comprising a tread portion, a pair of sidewall portions, a pair of bead portions, a radial carcass extending between a pair of bead cores embedded in the respective bead portion to reinforce these portions and having a turnup portion wound around the bead core from an inside of the tire toward an outside thereof, a bead filler rubber of a triangular shape at section taperingly extending from the bead core toward an end of the tread portion, and one or more reinforcing cord layers arranged at a side face zone ranging from the bead portion to the sidewall portion, in which the reinforcing cord layer is a layer of one or more rubberized cords spirally wound about an axial line of the tire and has an inner end in a radial direction of the tire between a position located outward from an outer periphery of the bead core in the radial direction and a position located inward from a tapered end of the bead filler rubber in the radial direction.
In a preferable embodiment of the invention, the inner end of the reinforcing cord layer is located in a position separated from the outer periphery of the bead core by a distance in the radial direction corresponding to 3-50% of a tire section height.
In another preferable embodiment of the invention, an outer end of the reinforcing cord layer in the radial direction is located in a position separated from a rim diameter line by a distance in the radial direction corresponding to 10-75% of a tire section height.
In the other preferable embodiment of the invention, the cord of the reinforcing cord layer is a cord selected from nylon cord, polyester cord, rayon cord, aramid cord and steel cord.
In a further preferable embodiment of the invention, the reinforcing cord layer has an end count of 15-60 cords/5 cm.
In a still further preferable embodiment of the invention, the bead filler rubber has a JIS hardness at 30xc2x0 C. of 65-83.
In the other preferable embodiment of the invention, an end of the turnup portion of the radial carcass has a height in the radial direction corresponding to 5-45% of the tire section height.
In a further preferable embodiment of the invention, the reinforcing cord layer is arranged along an outside of the turnup portion of the radial carcass or along an inside of the turnup portion of the radial carcass.
In a still further preferable embodiment of the invention, an outer end of the reinforcing cord layer in the radial direction exceeds an end of the turnup portion of the radial carcass in the radial direction.
In another preferable embodiment of the invention, a reinforcing sheet rubber extending toward the end of the tread portion is arranged along a tapered end portion of the bead filler rubber so as to contact therewith and has an even thickness of not more than 2 mm.
In the other preferable embodiment of the invention, an outer end of the reinforcing sheet rubber in the radial direction is located in a position separated from the rim diameter line to 30-75% of the tire section height.
The term xe2x80x9ctire section heightxe2x80x9d used throughout the specification means xe2x80x9ca half of a difference between an overall diameter of a tire and a rim diameter when the tire is mounted onto an approved rim and inflated under a specified air pressure without loadingxe2x80x9d as defined in JATMA YEAR BOOK (1999). And also, the term xe2x80x9crim diameter linexe2x80x9d used herein means a straight line passing through a position corresponding to a rim diameter and in parallel to an axial line of the tire. Furthermore, the term xe2x80x9cJIS hardnessxe2x80x9d used herein means a hardness of rubber measured according to JIS K6253-1993.